The student Unai Morales Diez obtained the qualification 'CUM LAUDE'.

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The student Unai Morales Diez obtained the qualification 'CUM LAUDE'.

THESIS

The student Unai Morales Diez obtained the qualification 'CUM LAUDE'.

2021·11·10

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Thesis title: Development of 3D Printed Continuous Fiber Composite Structural Components for Energy Absorption in case of Impact

Court:

  • Chairmanship: Carlos Daniel González Martínez (Universidad Politécnica de Madrid)
  • Vocal:Isabel Harismendy Ramírez de Arellano (Tecnalia Research & Innovation)
  • Vocal:Alberto López Arraiza (UPV/EHU)
  • Vocal: Rubén Ansola Loyola (UPV/EHU)
  • Secretary:Laurentzi Aretxabaleta Ramos (Mondragon Unibertsitatea)

Abstract:

  • The generation of knowledge about future materials and manufacturing processes will serve to develop high value-added products that respond to major societal challenges. Product customization, digitalization of manufacturing or the circular economy are some of these challenges that additive manufacturing (AM) can respond to.
  • Sustainable design is currently one of the guidelines in the development of automotive components, with lightweight design, energy savings and efficient use of raw materials being the subject of much research. In parallel to environmental concerns, safety remains a critical factor, and manufacturers must strive to ensure or improve the safety of vehicle occupants in impact situations. Therefore, the increase of energy absorption properties by means of complex structure design and non-conventional fiber orientations in cFRTP composite material is the main objective of the present thesis. For this purpose, new concepts of structures and metamaterials with predefined or programmable properties covering specific needs/functionalities within the vehicle structure have been analyzed and developed by means of composite AM technologies.
  • 3D printing - FFF of continuous fiber presents greater design freedom and flexibility in terms of fabrication of cFRTP structures as it allows to orient the fiber in the direction of the load, increasing its performance and material utilization.
  • The present work has focused on the generation of knowledge in three fundamental blocks:
  • The first block has focused on increasing the energy absorption properties of fabricated structural components through geometric profile design and selection of continuous fiber printing trajectories. For this purpose, the microstructural characterization and identification of printing defects due to the FFF process has been carried out and the relationship between geometry (fold profile), fiber printing pattern and nature of the reinforcement filament (cCF/PA, cGF/PA and cKF/PA) in the generation of these defects has been analyzed. At the same time, the fracture mechanisms that induce stable collapse modes of the printed profiles have been identified, analyzing the position and typology of the defects and their relationship with the load direction. All this, in order to convert a weakness/discontinuity in the structure (printing defects) into initiators of stable collapse.
  • In the second block, the response of printed materials reinforced with continuous fiber cFF (carbon, glass and Kevlar©) at different test speeds has been studied. On the one hand, it has been proved that there are differences in the nature of the PA matrices that cover the fibers and that explain their greater sensitivity to the strain rate and improvement of their impact resistance (Kevlar©). On the other hand, it has been proved that poor impregnation of the fibers or lack of consolidation of the printing material causes certain failure mechanisms based on fiber fracture, delaminations and friction between the layers and the printing cords.
  • The third block has been oriented to the identification and characterization of auxetic filling structures that improve the transverse behavior of the tubular profile, and that produce a synergistic effect on the absorption capacity of the profile-core binomial. In addition, it has been shown that the collapse mode of the auxetic core (star-like reentrant) increases the load capacity of the profile and controls its progressive collapse mode while densifying it.